The present invention relates to implantable medical device systems, and more particularly to Implantable Cochlear Stimulation (ICS) systems. ICS systems are used to provide the sensation of hearing to those who are profoundly deaf, and for whom traditional hearing aids are of little or no assistance due to disease or damage to the middle ear or inner ear. An ICS system provides the sensation of hearing by applying electrical stimuli to the inside of the scala tympani duct of the cochlea, thereby directly stimulating the ganglion cells coupled to the auditory nerve. Once stimulated, such ganglion cells send nerve impulses to the brain through the auditory nerve, and the impulses are sensed in the brain as perceived sound.
ICS systems typically include implantable and external components. The implantable components include a receiver, an implantable pulse generator and an electrode array, which electrode array is inserted into the cochlea, through which the electrical stimuli are applied. The external components include a power source, a microphone, a speech processor, and a headpiece. The microphone senses sound waves in conventional manner and converts such sensed sound waves to an electrical signal. The electrical signal is then processed by the speech processor and converted into an appropriate control signal that is transmitted to the implantable receiver/stimulator. A representative implantable cochlear stimulation system is described in U.S. Pat. No. 5,776,172, issued Jul. 7, 1998 for xe2x80x9cMultichannel Implantable Cochlear Simulator,xe2x80x9d incorporated herein by reference.
In operation, the power and control signals are transmitted to the implantable receiver/stimulator through a primary coil located in the headpiece, and are received through a secondary coil included within the implantable receiver/stimulator. In order to operate efficiently, i.e., in order for the headpiece to be able to transcutaneously (i.e., through the skin) transmit the control signal to the implantable receiver/stimulator, it is necessary that the primary coil in the headpiece be placed in close alignment with the secondary coil in the implantable receiver/stimulator.
The most common technique for retaining the headpiece of a transcutaneous-type implantable cochlear stimulation system is the use of two permanent magnets. One magnet resides in the implantable receiver/stimulator near the center of the secondary coil. The other magnet resides in the headpiece near the center of the primary coil. The use of magnets to retain the headpiece is very simple, effective, and cosmetically attractive. However, there are several drawbacks to this method of headpiece retention. Some users have thick skin flaps that increase the separation of the magnets and reduce their attracting force. Physically active children and adults have found magnetic headpiece retention insufficient. Additionally, the internal magnet may interfere with MRI (magnetic resonance imaging) diagnosis.
Another method of retaining a head piece is by using VELCRO(copyright) pads as described in U.S. Pat. No. 5,545,191, dated Aug. 13, 1996 for xe2x80x9cMethod for Optimally Positioning and Securing the External Unit of a Transcutaneous Transducer on the Skin of a Living Body.xe2x80x9d The ""191 patent describes several embodiments with different shaped VELCRO(copyright) pads. While the use of VELCRO(copyright) pads provides some advantages, it also has several drawbacks. The use of VELCRO(copyright) pads to retain the headpiece requires that either the hook or loop VELCRO(copyright) pad be semi-permanently attached to the skin with several adverse results: the long term attachment to the skin of such pad may cause irritation or itching, the pads attached to the skin may be snagged when the user is combing or brushing their hair, the user""s hair may also become tangled in the VELCRO(copyright) pads, and the extraction of the hair from the VELCRO(copyright) pads may cause significant discomfort. In addition to these ergonomic factors, the thickness of the VELCRO(copyright) pads may reduce the efficiency of the inductive coupling between the primary coil in the headpiece and the secondary coil in the implantable receiver/stimulator. Efficient power use in ICS systems is a significant issue, thus it is important that the primary and secondary coils be as close as possible. Further, if either the VELCRO(copyright) pad should become soiled, or if a user participates in work related or recreational activities that tend to soil or otherwise degrade the VELCRO(copyright) pads, frequent replacement of the VELCRO(copyright) pads may be required.
Yet another method of retaining a headpiece is using a hair-clip as described in U.S. Pat. No. 6,275,736 issued Aug. 14, 2001 for xe2x80x9cHair Clip Retention System for Headpiece of Cochlear Implant System,xe2x80x9d assigned to the assignee of this application. The ""736 patent describes a hair-clip that avoids many of the disadvantages of a magnet retention system or a VELCRO(copyright) pad retention system. However, in some uses, the hair-clip of the ""736 patent may result in the headpiece cable projecting from the headpiece case in an undesirable direction, wherein the cable may present a cosmetically undesirable appearance, or the cable may project away from the head and interfere with hats or snag on surrounding objects.
Therefore, there is a need for a low cost, robust, cosmetically acceptable, and comfortable alternative solution for holding the headpiece of an implantable cochlear stimulation system in close alignment with the secondary coil included in an implantable stimulator, that allows the headpiece to be rotated to a desired position.
The present invention addresses the above and other needs by providing an improved hair-clip for rotatably securing a headpiece of an Implantable Cochlear Stimulation (ICS) system, adjacent to an implantable device of the ICS system. The hair-clip includes three fingers to securely grasp the headpiece, while allowing rotation of the headpiece relative to the hair-clip. Both power and control signals are transmitted transcutaneously from a primary coil in the headpiece to a secondary coil in the implantable device. Efficient transmission of these signals requires that the headpiece be securely held in close alignment to the implantable device. The improved hair-clip securely holds the headpiece in place, and allows the headpiece to be rotated to position the headpiece cable.
In accordance with one aspect of the invention, there is provided an ability to rotate the headpiece relative to the hair-clip. The ability to rotate the headpiece allows a user to position the headpiece cable-to achieve a comfortable and inconspicuous cable routing. The improved hair-clip of the invention is adaptable to known headpieces, and results in a minimal cosmetic change.
It is a further feature of the present invention to provide retention of the headpiece regardless of the presence of skin flaps. A thick skin flap often results in excessive physical separation of the magnets in known ICS systems, thus preventing the magnets from attracting each other with adequate force to retain the headpiece in its desired position. The hair-clip does not rely on magnetic attraction of the headpiece to the implantable device, and thereby provides headpiece retention regardless of skin flap thickness.
It is an additional feature of the present invention to provide robust retention of the headpiece. Magnetic headpiece retention provides limited retaining force. When subjected to strenuous activities, magnetic retention is likely to fail to retain the headpiece. The hair-clip of the present invention may be used with magnetic retention, or alone, to provide adequate retention during periods of increased activity. When the invention is used in a magnet-less headpiece retention system, additional space is provided for electronics in both the headpiece and in the implantable device.
It is another feature of the invention to provide a headpiece retention method that does not require a magnet in the implantable device. The presence of a magnet in an implantable device may interfere with MRI examinations. The invention thus provides headpiece retention without such interference.